CEUTA, Spain/FNIDEQ, Morocco—Hundreds of migrants tried to force their way past tightened security into Ceuta on May 19, as Spain pressed on with the expulsion of thousands who had swum or climbed into its North African enclave over the past two days. Around two-thirds of the roughly 8,000 migrants who made it to Ceuta, including unaccompanied children, have been expelled, Spanish authorities say, though many of those returned said they would again try to reach Europe. As thousands gathered in the Moroccan border town of Fnideq, near the frontier with Ceuta, hundreds of them clashed after dark with Moroccan riot police, throwing stones and setting on fire a motorbike and a trash bin, a Reuters witness said. The rush of migrants began on May 17 when Morocco appeared to loosen border controls, a move widely interpreted as retaliation for Spain’s hosting of a Western Sahara independence leader. As dense afternoon …